Christchurch pig farmers accused of keeping their animals in squalid, overcrowded living conditions believe they are victims of a setup.

Current affairs show Sunday this week revealed controversial footage, which activist group Farmwatch says it filmed earlier this year at Richard and Nicola Chilton's Belfast piggery, showing severe overcrowding and sows in a farrowing crate so small that newborn piglets were squashed to death.

Other piglets lay dying next to their helpless mother while other animals had infected eyes and obvious sores. It also showed a dead pig that had been left to rot among living pigs and dozens of rats running over the animals.

When approached by The Press at the farm this week, Nicola Chilton questioned the legitimacy of the footage.

The couple do not believe the worst of the video was shot at their property.

"Do you think we would have been farming for 35 years if [the farm] run in a poor fashion?

"Why were [Farmwatch] here two nights in a row? Did they chuck a bag full of rats on our property?"

Ministry for Primary Industries officials visited the farm last week after being shown the footage by TVNZ and the animals were "assessed as being generally in good health".

"There was no evidence of some of the detail shown in the video footage - for example, there were no dead animals observed," the MPI said.

"Did MPI see any rats on the day they came? I think the answer is no. [MPI said] there's no animal welfare issues and that's what the [PigCare] auditor said."

She declined to answer further questions.

Farmwatch spokeswoman Jasmine Gray said all the video and photos were from the same farm.

"Because pig farms are quite different around the country, it's quite easy to identify the different building structures on [Chilton's] farm in the photos," she said.

The farrowing crates were on a diagonal angle, which they had not seen before at other pig farms.

The video was a compilation shot over two consecutive nights in April because additional footage was needed, Gray said.

She rejected the suggestion the rats were planted by Farmwatch.

Gray stressed the expose was about raising awareness of industry-wide issues, not vilifying individual farms.

"Most of our investigators have been working for at least 10 years going into farms all over the country . . . and this pig farm isn't the only one that looks like that."

The New Zealand Pork Board this week confirmed meat supply from the farm was stopped after its PigCare rating was changed from green to amber in May - a month after the Farmwatch footage was obtained. It remains amber.

It would not comment on the Chiltons' claims.

Board chairman Ian Carter earlier said the farm featured in the programme was not condoned by the industry and was not typical of a New Zealand commercial pig farm.

It had been in contact with the farmer and "we are willing to engage in whatever process is required to resolve the issues surrounding this farm", he said.